This invention relates to an electron beam type pattern transfer apparatus for transferring a mask pattern onto a substrate in a vertical magnetic field created by focusing magnets having superconductive coils.
As a conventional electron beam type pattern transfer apparatus an apparatus is known which exposes a substrate to the scanning of an electron beam to form a resist image thereon which corresponds to a predetermined pattern. However, the apparatus requires a long time for the scanning of the electron beam, resulting in lower productivity. There is also an apparatus for illuminating with an X-ray or an electronic ray a mask on which a predetermined pattern is formed and transferring the predetermined pattern to a substrate. Where, however, an X-ray is used, the resist layer suffers a lower sensitivity and, moreover, an X-ray source is expensive and dissipates more power. Where the electronic ray is used, a hollow mask and a corresponding lens system are required, resulting in an expensive apparatus. A pattern transfer apparatus using a photoelectric mask is also known in the art. In order to obtain better resolution it is necessary to provide a uniform focusing magnetic field over a wide range between a photoelectric mask and a substrate. However, it has been difficult to provide such a magnetic field. Now suppose that the thickness of a resist layer on the substrate is 1 .mu.m, a value necessary for the manufacturing process of an LSI, that the distance between the photoelectric mask and the substrate is made as small as permitted for a high accuracy of exposure, for example, 5 mm and that the intensity of a magnetic field required, when the acceleration voltage of the electron beam between the photoelectric mask and the substrate is above 20 kV, is about 3 KG. In this case, it would be very difficult to obtain a magnetic field by using a focusing magnet which is constituted of an air-core coil of normal electric conductors. In order to obtain a magnetic field of 3 KG it is necessary to significantly increase the ampere turns of the coil. However, there is a problem caused by the generation of heat resulting from the distribution of the winding and the internal resistance, because of the bulkier apparatus. Even if such a bulkier apparatus is implemented, it would be difficult to obtain a uniform magnetic field over a wide area. Stabilization of the magnetic field is also required. Even if objective can be attained by stabilizing the current of the drive source of the focusing magnet, it would be impossible to keep the ripple components of the current of the drive source of the focusing magnet at a zero level. It is therefore next to impossible to generate a magnetic field satisfying the above-mentioned requirements. Recently, in the manufacturing process of an LSI the area of an electron beam resist to which an image is transferred has increased and it would be difficult to apply a uniform magnetic field on such a resist layer corresponding to a transfer pattern. This prevents improvement of the image resolution.